Functions defined by the POSIX standards for manipulating and querying the
file system. Names of underlying POSIX functions are indicated whenever
possible. A more complete documentation of the POSIX functions together
with a more detailed description of different error conditions are usually
available in the system's manual pages or from
http://www.unix.org/version3/online.html (free registration required).

When a function that calls an underlying POSIX function fails, the errno
code is converted to an IOError using errnoToIOError.
For a list of which errno codes may be generated, consult the POSIX
documentation for the underlying function.

Setting file modes

setFileMode path mode changes permission of the file given by path
to mode. This operation may fail with throwErrnoPathIfMinus1_ if path
doesn't exist or if the effective user ID of the current process is not that
of the file's owner.

Checking file existence and permissions

fileAccess name read write exec checks if the file (or other file system
object) name can be accessed for reading, writing and/or executing. To
check a permission set the corresponding argument to True.

Creation

createNamedPipe fifo mode
creates a new named pipe, fifo, with permissions based on
mode. May fail with throwErrnoPathIfMinus1_ if a file named name
already exists or if the effective user ID of the current process doesn't
have permission to create the pipe.

createDevice path mode dev creates either a regular or a special file
depending on the value of mode (and dev). mode will normally be either
blockSpecialMode or characterSpecialMode. May fail with
throwErrnoPathIfMinus1_ if a file named name already exists or if the
effective user ID of the current process doesn't have permission to create
the file.

getPathVar var path obtains the dynamic value of the requested
configurable file limit or option associated with file or directory path.
For defined file limits, getPathVar returns the associated
value. For defined file options, the result of getPathVar
is undefined, but not failure.

getFdPathVar var fd obtains the dynamic value of the requested
configurable file limit or option associated with the file or directory
attached to the open channel fd. For defined file limits, getFdPathVar
returns the associated value. For defined file options, the result of
getFdPathVar is undefined, but not failure.